Add linting CI

.gitlab-ci.yml

+---
+stages:
+  - linting
+
+cache:
+  paths:
+    - .cache
+
+ansible-lint:
+  stage: linting
+  image:
+    name: registry.gitlab.fachschaften.org/fsi-ansible/ci-docker-image:latest
+    entrypoint: [""]
+  script:
+    - ansible-lint -v --offline